Ever since the implementation of computers in geological exploration, it has been desirable to digitize the large amounts of data that are available only in analog form, for example of a hand picked horizon on a seismic section. However, existing devices for carrying out the digitizing have been unsatisfactory. Thus, for example, the typical mouse used with personal computers is entirely inadequate for digitizing since it lacks precision.
Also, table top systems presently employed for digitizing use large, transparent grid systems and a hand-held cursor with an induction coil for creating a current in the wires of the grid. These digitizers are cumbersome and difficult to use.
In another digitizer used for digitizing seismic sections, an optical sensor slides along a steel bar having an optical strip to determine points in the Y direction along the steel bar. In the X direction (next shot point) the steel bar must be moved by hand to the next trace.
Recently, there has been produced a planimeter which utilizes a pair of wheels, each with a rotary optical encoder, oriented parallel to each other. The planimeter responds to the differential movement of the dual rotary optical encoders as the wheels follow a trace.